Technetium radiopharmaceuticals now play a prominent role as diagnostic agents in nuclear medicine. However, little is known of the chemistry of technetium, particularly in its lower oxidation states. Increased knowledge of the coordination chemistry of this element should significantly aid the effort to develop tumor-specific radioscintigraphic agents. The goals of this proposed research are to: 1) explore the chemistry of the lower-oxidation states of technetium, and 2) to synthesize a series of radioscintigraphic tumor-diagnostic agents containing Tc-99m in the I to IV oxidation states. Coordination to pi-acceptor ligands will provide a means of stabilizing the Tc(I) and Tc(II) ions. These ions are expected to coordinate preferentially to nitrogen rather than oxygen ligands and so will differ in their mode of action from the presently employed Tc(IV) and Tc(VII) radiopharmaceuticals. Compounds will be initially synthesized with the long-lived isotope, Tc-99, so that analytical, spectroscopic, electrochemical and kinetic investigations can be made and rapid synthetic procedures developed. Potential tumor-diagnostic agents will fall into two categories: 1) those in which Tc(I) or Tc(II) ions should bind directly to target sites, and 2) those containing Tc(IV) firmly coordinated by ligands. The first class of compounds will contain groups which can dissociate from the metal and so leave sites open for direct coordination. Chemical modification of the non-leaving groups should provide a means for varying the substitution rates and reduction potentials of these complexes so that their in vivo binding rate can be controlled. The tumor specificity of the second category of complexes will depend largely on the attributes of the ligands. Complexing agents which are utilized by tumor tissue or are known to concentrate in cancers will therefore be employed.